In ink-jet printing methods, droplets of ink are directly projected onto a recording medium from very fine nozzles and allowed to adhere to the recording medium to form characters or images. The ink-jet printing methods have become rapidly spread because of various advantages such as easiness of full coloration, low cost, capability of using a plain paper as the recording medium, non-contact with printed characters or images, etc.
In recent years, in order to impart good weathering resistance and good water resistance to printed materials, an ink containing a pigment as a colorant has been extensively used.
On the other hand, it has been required to print characters or images on a recording medium for commercial printing purposes using a low-water absorbing coated paper such as an offset coated paper, or a non-water absorbing resin film such as a polyvinyl chloride resin film, a polypropylene resin film and a polyester resin film.
It is known that when characters or images are printed on the low-water absorbing or non-water absorbing recording medium by the ink-jet printing methods, there tend to occur problems such as prolonged drying time owing to slow absorption or no absorption of liquid components, and deterioration in quick-drying fixing properties of the ink upon printing the characters or images thereon. Furthermore, it is also known that when printing characters or images on such a low-water absorbing recording medium, the pigment as a colorant of the ink tends to remain on a surface layer of the recording medium, thereby causing deterioration in long-term fixing properties of the ink.
In order to improve fixing properties of the ink on the low-water absorbing or non-water absorbing recording medium, various studies for incorporating resin particles into the ink have been made conventionally. For example, in JP 2004-176057A, it is described that by incorporating resin particles having a specific Tg value into an ink, it is possible to achieve improvement in fixing properties of a colorant in the ink on a hydrophobic non-water absorbing recording medium. In Examples of JP 2004-176057A, it is also described that N-methyl pyrrolidone, polyethylene glycol, ethylene glycol, glycerol, 2-pyrrole, 1,2,6-hexanetriol or the like is used as an organic solvent for the ink. In addition, JP 2013-216864A discloses an aqueous ink-jet ink including water, a pigment, water-dispersible resin particles as a binder resin, and two or more kinds of specific water-soluble organic solvents, which is excellent in printability to a highly-hydrophobic less-absorptive base material such as a coated paper, an art paper and a polyvinyl chloride sheet, ejection stability through ink-jet nozzles, storage stability and coating film durability. In addition, in JP 2013-216864A, it is also described that (poly)propylene glycol alkyl ethers and alkane diols are used as the aforementioned water-soluble organic solvents.